The present invention relates to a process for manufacturing a tire comprising a carcass reinforcement, the reinforcement elements of which are radial in the sidewalls and oblique to the circumferential direction in the region of the crown reinforcement. It also relates to the tires obtained by said process.
Tires of the radial type, and more precisely the non-vulcanized toric blanks thereof, are commonly manufactured by a process comprising two distinct phases. In the first phase, the cylindrical blank of the carcass reinforcement is manufactured on a cylindrical building drum. The blank comprises, inter alia, the carcass reinforcement itself, the rubbers and reinforcements internal to the carcass reinforcement, and all of the elements forming the beads, these elements being the bead wires, the profiled elements and bead filler layers and bead reinforcement armatures. In a second phase, the cylindrical blank of the carcass reinforcement is shaped, dilated to adopt a toric form, on which form there will then be laid the elements constituting the crown reinforcement, the profiled elements and rubber layers separating the crown reinforcement from the carcass reinforcement, as well as the tread. The toric, non-vulcanized tire blank is then introduced into a vulcanization mold, the blank undergoing slight additional shaping to end up with the final dimensions of the tire.
The two-phase manufacturing process for radial tires has for a long time been considered as the only one which can be used industrially, despite the fact that, if compared to the single-phase (or -stage) process used for cross-ply tires, the two-stage process involves additional, more complex, more costly equipment, more labor, and consequently a necessarily higher cost price.
That is why it has always been considered advantageous to be able to manufacture radial tires by a single-stage process and using the traditional equipment for manufacturing cross-ply tires. Such single-stage process consists of assembling, on one and the same drum, all of the constituents of the tire blank in a practically cylindrical shape.
To the extent that the reinforcement elements of the carcass reinforcement are elements which are radial over the entire meridian length and that the crossed reinforcement elements of the crown reinforcement create a triangulation with the elements of the carcass reinforcement, the shaping of the cylindrical blank to arrive at a toric blank is practically impossible, unless a certain number of tricks are used such as lubricating the different layers and/or plies by means, for example, of zinc stearate in powdered form or in solution in a solvent, or the laying between the carcass reinforcement and the crown reinforcement of a large pad of rubber mix. These tricks having more drawbacks than advantages.
French Patent 1 413 102, noting that the portion of the radial carcass reinforcement located radially to the inside of the crown reinforcement might be superfluous, describes a tire comprising a carcass reinforcement anchored in each bead to an inextensible annular element and formed of independent reinforcement elements. The independent reinforcement elements are arranged, firstly, radially or substantially radially between the bead and the crown reinforcement and, secondly, with an orientation which moves substantially away from the radial orientation over at least an axial portion of the region in which the crown reinforcement extends. The carcass reinforcement is finished off by a crown reinforcement, and the simplest solution consists in having a crown reinforcement composed of a single crown ply formed of reinforcement elements, the angle of orientation of which relative to the circumferential direction is of a sign opposite to that formed by the elements of the carcass reinforcement in its oblique portion. Such a tire structure can be produced by the one-stage manufacturing process. The carcass ply is arranged on a building drum, the radial reinforcement elements of the carcass ply being placed substantially parallel to the generatrices of the drum. The bead wires are then put in place and the edges of the carcass ply are turned up around the bead wires and bead filler rubbers to form the carcass ply upturns. Then the crown ply is laid, the direction of the crown reinforcement elements forming a suitable angle with those of the carcass ply, and the two plies, carcass and crown, are caused to adhere. Then the cylindrical blank thus obtained is shaped by bringing together the bead wires and inflating the membrane of the building drum. The reinforcement elements of the carcass ply and those of the crown ply adopt a new angular configuration depending on the starting angles and the shaping ratio in the zone where the two plies are superposed, whereas the carcass ply elements substantially retain their radial orientation in the sidewalls.
Although the foregoing process can effectively make it possible to obtain blanks having a plurality of carcass reinforcement plies and a plurality of crown reinforcement plies, the reinforcement elements of the plies can only have two angular orientations (xe2x88x92xcex2, +xcex3) or (+xcex2, xe2x88x92xcex3) at the crown, without such orientations being identical (xcex2xe2x89xa0xcex3). The process, therefore, does not make it possible, firstly, to obtain a tire having a single crown ply which is exempt from excessive lateral thrust at 0xc2x0 drift, and, secondly, to have a tire which is effective in all travelling configurations, owing to the fact that the orientation of the elements of the different plies does not result in the creation of the slightest axial zone with the presence of a triangulated reinforcement. It is true that the cited reference proposes a solution for overcoming the last-mentioned disadvantages, i.e., it is possible to add to the structure described another crown ply, the reinforcement elements of which have an orientation of a sign which is opposite to that of the reinforcement elements of the first ply. The laying of the second crown ply, however, is only effected, according to the process described, in a second stage after shaping to the final diameter of the toric blank, that is to say, a process identical to the process for manufacturing a blank having a true triangulated reinforcement.
It is an object of the invention to overcome the foregoing disadvantages and to provide a tire produced by a process very close to a one-stage process, and which makes it possible to obtain either a tire having a crown ply, the reinforcement elements of which form the angle opposite to that of the elements of the radially subjacent carcass with the circumferential direction, or a tire having a crown reinforcement with plies of reinforcement elements which are crossed from one ply to the next, or a tire having a partially triangulated crown reinforcement.
According to the invention, a process for manufacturing a tire comprising a carcass reinforcement which is radial in the sidewalls and the reinforcement elements of which form with the circumferential direction and radially beneath a crown reinforcement, which is composed of at least one layer of reinforcement elements forming an angle xe2x8axa5xcex32 with said direction, an angle ∓xcex22 over a width L, includes initially manufacturing a cylindrical blank comprising all of the components of the tire by at least the following steps:
a) at least one carcass reinforcement ply formed of radial reinforcement elements is laid on the central part of diameter D of a cylindrical building drum;
b) the annular bead elements, which are inextensible and have an internal diameter D3, the profiled elements and bead filler rubbers, the bead reinforcement armatures, are laid, and the edges of the carcass ply are turned up to form the carcass upturns;
c) the central part of the carcass ply is subjected to an angular variation of its reinforcement elements by pre-shaping on the drum, passing from the diameter D to a greater diameter D1, such that the radial elements become oblique, forming with the circumferential direction an angle ∓xcex21, such angular variation of the carcass ply on the width L being effected by means of at least one auxiliary ply N of width L0, referred to as a shaping ply, which is formed of textile or metallic elements coated in a vulcanized rubber mix and laid on the building drum for the cylindrical tire blank;
d) the profiled elements and rubber layers are laid between the carcass reinforcement and crown reinforcement, then radially to the outside at least one crown ply formed of reinforcement elements oriented relative to the circumferential direction by the angles xc2x1xcex31 ∓xcex31), xcex31 being such that |xcex31|xe2x88x92|xcex21|xe2x89xa67xc2x0;
e) it is finished by laying the rubber mixes of the tread and it is shaped by bringing the internal diameter D1 of the cylindrical blank to the internal diameter D2, which is the diameter of the toric blank of the tire in the vulcanization mold and of the vulcanized tire.
The diameter D1 is, firstly, greater than the diameter D of the building drum and, secondly, is between 0.95 times and 1.3 times the internal diameter D3 of the annular bead elements. The angular variation of the carcass ply over the width L is effected by means of at least one auxiliary ply of width L0, the reinforcement elements of which form an angle xc2x1xcex1 with the circumferential direction.
Preferably, the angular variation of the radial carcass reinforcement will be effected by means of a cylindrical sleeve which is vulcanized and formed of two auxiliary plies, the reinforcement elements of which form angles equal respectively to 90xc2x0 and xc2x1xcex1 or xc2x1xcex1 and 90xc2x0 with the circumferential direction.
Advantageously, the crown ply (plies) laid on the diameter D1 will have a width (widths) L311 and (L322) greater than the width L1 of the ply for shaping to the diameter. The tire thus obtained by a process which can be called a one-stage process has the advantage of having a carcass reinforcement which is radial in the sidewalls and oblique radially beneath the crown reinforcement, having beneath the edges of the reinforcement an obliqueness which is variable and increases axially towards the edges of the reinforcement over an axial width L322-L1, which makes it possible, in the case of a crown reinforcement having two plies and for said axial width, to obtain triangulation of the two edges of the reinforcement which is beneficial to the performance of the tire during travel.
The performances will be improved if the two crown plies of width L31 and L32 are preferably replaced by a single ply of elements which are oriented at the angle xc2x1xcex31 and of width L11, and the edges of which are turned up on themselves, the presence of the upturn being sufficient to create triangulation on the edges of the crown reinforcement and furthermore providing, as is known per se, additional rigidity to said edges.